THE ROTATION CURVE OF THE GALAXY OBTAINED FROM PLANETARY-NEBULAE AND AGB STARS

The rotation curve of the Galaxy is obtained from a sample of planetar y nebulae and asymptotic giant branch (AGB) stars. The AGE stars are O H/IR stars and carbon-rich stars with large mass-loss rates, with velo cities known from radio observations and distances determined from the ir infrared luminosity. The rotation curve exhibits a steep decrease i n the solar vicinity, and a minimum at about 8.5 kpc (adopting R circl e dot=7.9 kpc). WE fit the rotation curve with a mass distribution mod el of the Galaxy, based on the model for star counts in the infrared r egion of Ortiz & Lepine; the main components are a spherically symmetr ic density distribution that represents the bulge and the halo, and tw o exponential disc components with scalelengths 2.6 and 4.5 kpc. A goo d agreement is found between the star count model and the rotation cur ve. A minimum is observed at 8.5 kpc; possible explanations are discus sed. The surface density of the disc in the solar neighbourhood is 77 M circle dot pc(-2), not very different from the value predicted by st ar counts. This result implies that there is no need for a dark matter component, at least up to a radius of about 12 kpc.